Chemokines comprise a family of soluble factors with diverse effects on leukocyte function. Several chemokines have been implicated in regulating adhesion of lymphocytes to vascular endothelium and stimulating transmigration into lymph nodes. This proposal centers on the function of several recently identified chemokines, particularly stromal cell-derived factor-1 (SDF-1), which are potent chemoattractants of recirculating lymphocytes. The effects of SDF-l on regulating lymphocyte binding and migration across vascular endothelium and on lymphoid stroma will be examined. The approach will be initially to determine the microexpression of SDF-1 and other lymphocyte chemokines within lymphoid tissue and blood vessels. Effects of SDF-1 on activation of known adhesive interactions will then be tested with static binding assays. The mechanism of any SDF-1 induced alterations in adhesive interactions will be pursued. In addition, dynamic flow assays will be used to dissect the effects of SDF-1 and other chemokines on the distinct steps of lymphocyte tethering, rolling, firm attachment and transmigration. These studies will test the effects of chemokines on lymphocyte binding under flow to purified endothelium and stromal cells as well as frozen tissue sections. The goal of this proposal is to gather additional information on the role of chemokines, particularly SDF-1, in regulating lymphocyte adhesion and migration.